The present invention relates to a photosensitive member for electrophotography, and more particularly to a high-sensitivity photosensitive member for electrophotography having a photosensitive layer containing an organic photoconductive material.
The photosensitive layers of photosensitive members for electrophotography were conventionally made from inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, etc. However, selenium not only needs to be recovered as a toxic material but also has poor heat resistance because it is crystallized by heat. Cadmium sulfide also needs to be recovered as a toxic material and has poor humidity resistance. As for zinc oxide, it has poor humidity resistance and insufficient durability for repeated copying. Thus, efforts have been made to develop new photosensitive members.
Recently, research has been advanced on organic photoconductive materials for use in the photosensitive layers of electrophotographic photosensitive members, and some of them have been put into practical use. The organic photoconductive materials are superior to the inorganic counterparts in that the former is lighter, easier to form into films, easier to manufacture photosensitive members and even capable of providing transparent photosensitive members depending on the types thereof.
Despite these advantages, the organic photoconductive materials have not been widely used for photosensitive members for electrophotography, because they are inferior to the inorganic counterparts with respect to sensitivity and durability.
What has recently become a main stream of development is a so-called separated function-type photosensitive member in which different compounds separately bear the functions of generating and transporting charge carriers, since such function separation is highly effective for increasing sensitivity. This type of the organic photosensitive members have also been put into practical use.
Useful as charge carrier-transporting media are high-molecular, photoconductive compounds such as polyvinyl carbazole, and low-molecular, photoconductive compounds dispersed in polymer binders.
As for organic, low-molecular, photoconductive compounds, they can easily provide photosensitive members having excellent mechanical properties because their binders can be selected from polymers having good film-forming properties, flexibility and adhesion. Nevertheless, it was difficult to find out compounds suitable for producing photosensitive members with sufficiently high sensitivity.